A lot of methods have been proposed for acquiring waveform information on radio waves, sound waves, etc. using a sensor such as a radar, sonar or lidar and determining spatial distribution of wave source intensity.
There exist a variety of methods, such as the beam former method, as described in Non Patent Literature 1, for example. In a technique described in the Non Patent Literature 1, distribution in each direction at a point in time is acquired along a time series and arrival time of each wave is converted into distance from the sensor based on the velocity of the wave, by which spatial distribution (direction vs. distance) can be acquired. Further, by arranging the spatial distributions in order of the time series, temporal distribution can be acquired.
In order to achieve high directivity, many of the aforementioned methods adjust the phase of each piece of waveform information acquired from each sensor element of the sensor in consideration of the shapes and relative positions of the sensor elements.
Meanwhile, such waveform information, which was generally processed as an analog signal continuous on the time axis, recently tends to be sampled discretely on the time axis and processed as a digital signal. The processing of the waveform information as a digital signal made it possible to employ a variety of complicated algorithms with ease. The method described in the Non Patent Literature 1 was also designed taking the digitization into consideration.